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Microtubule-targeting drugs induce bcl-2 phosphorylation and association with Pin1

N Pathan1, C Aime-Sempe, S Kitada

  • 1The Burnham Institute, 10901 N. Torrey Pines Rd., La Jolla, CA 92037, USA.

Neoplasia (New York, N.Y.)
|January 5, 2002
PubMed

Insights

Bcl-2 phosphorylation by Cdc2 kinase, triggered by microtubule-targeting drugs, may inactivate its anti-apoptotic function. This phosphorylation leads to Pin1 interaction, potentially altering Bcl-2

Area of Science:

  • Molecular Biology
  • Cancer Research
  • Cell Cycle Regulation

Background:

  • Bcl-2 is a key apoptosis suppressor overexpressed in cancers.
  • Microtubule-targeting drugs induce Bcl-2 phosphorylation, reducing its anti-apoptotic role via unknown mechanisms.
  • Understanding Bcl-2 regulation is crucial for cancer therapy development.

Purpose of the Study:

  • To elucidate the mechanism of Bcl-2 inactivation by microtubule-targeting drugs.
  • To identify the kinase responsible for Bcl-2 phosphorylation and the specific phosphorylation sites.
  • To investigate the functional consequences of Bcl-2 phosphorylation, including protein interactions.

Main Methods:

  • Pharmacological inhibition of serine/threonine-specific protein kinases.
  • Co-immunoprecipitation assays to identify interacting proteins.
  • Site-directed mutagenesis (serine to alanine substitutions) to map phosphorylation sites.
  • Analysis of protein-protein interactions using co-immunoprecipitation.

Main Results:

  • Flavopiridol, a cyclin-dependent kinase inhibitor, selectively blocked Bcl-2 phosphorylation induced by antimicrotubule drugs.
  • Cdc2 kinase was identified as a potential phosphorylating agent for Bcl-2 in M-phase-arrested cells.
  • Serines 70 and 87 were identified as major phosphorylation sites on Bcl-2.
  • Phosphorylated Bcl-2 associated with Pin1, a peptidyl prolyl isomerase, but not with other known binding partners like Bax or BAG1.
  • Phosphorylation did not affect Bcl-2 homodimerization or binding to Bax, BAG1.

Conclusions:

  • Cdc2-mediated phosphorylation of Bcl-2 at serines 70 and 87 by microtubule-targeting drugs may lead to its functional inactivation.
  • The interaction of phosphorylated Bcl-2 with Pin1 suggests a role for Pin1 in modulating Bcl-2's anti-apoptotic activity.
  • This mechanism provides a novel target for cancer therapies aimed at reactivating apoptosis in tumor cells.

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